Preloading HTML5 Audio in Mobile Safari

问题

I'm having a problem preloading HTML5 audio content and then using what I have in cache rather than attempting to redownload the audio every time I try to replay it.

http://cs.sandbox.millennialmedia.com/~tkirchner/rich/K/kungFuPanda2_tj/

The experience is suppose to be that when someone clicks on the banner, it pops up an ad with a loading bar. THe loading bar is loading all the images necessary for the animation. In the meantime, the audio is also getting loaded via audio tags already on in the DOM (which is fine). After all the images are loaded, the loading bar disappears and the user can continue on. There are 4 buttons on the bottom of the screen that they can click. Clicking one of them plays the audio file and images do a flipbook-style animation thats synced to the audio.

Audio Tags:

<audio id="mmviperTrack" src='tigress.mp3'></audio>
<audio id="mmmantisTrack" src='viper.mp3'></audio>
<audio id="mmtigressTrack" src='kungfu3.mp3'></audio>
<audio id="mmcraneTrack" src='crane.wav'></audio>

Play Button Event Listeners:

button.addEventListener('click',function(){
    if ( f.playing ) return false;
    f.playing = true;
    button.audio.play();
},false);

button.audio.addEventListener('playing', function(){
    animate();
}, false);

The problem is, in javascript, everytime I click play(), it reloads the audio file and then plays it. I can't seem to get it to load the audio once in the beginning and go off of whats stored in memory rather than try to reload the audio every single time I click the button.

I've tried experimenting with the preload and autobuffer properties, but it seems that mobile safari ignores those properties, because no matter what I set them too, the behavior is always the same. I've tried experimenting with source tags and different file formats... nothing.

Any ideas?

回答1:

Alright, so the solution was a bit of a hack, cheat, workaround, whatever you want to call it.

What I noticed is that if I hit the play button on an audio file that I just played, it doesn't reload itself. It could be because I paused the audio after it finished playing through, but I'm not 100% sure on that. In any case, what I did is I combined all 4 audio files into one large audio file (yay Audacity~!). Then, every time I hit one of the play buttons I would set the currentTime property of the audio object to whatever the starting point of that track and then play the track until it hit its ending point, and then pause it again. Mission accomplished! Loaded once in the beginning and never again for each play.

Not crazy about the idea that I had to combine all the different audio tracks, but hey it works.

Oh, also. To get the audio track to load and fire a "canplaythrough" event, I attached this function to a user click event:

var track;
function addHTMLAudio() {
    track = document.createElement('audio');
    track.id = 'mm_audio'
    track.autoplay = false;
    track.preload = false;
    track.addEventListener('canplaythrough',function(){
        track.removeEventListener('canplaythrough');
        audioLoaded = true;
    },false);       
    document.getElementById('body').appendChild(track);
    track.src = f.trackURL;
    track.play();
    setTimeout(function(){ track.pause();  },1);
}

playButton.addEventListener('click',function(e){
    if ( playStatus > 0 ) return;
    playStatus = 1;

    var myId = e.target.parentNode.id;
    var myClip = findClip( myId );

    myClip.state = 'active';        
    track.currentTime = myClip.tIndex.start;

    track.play();
    runAnimation(myClip);       
},false);

来源：https://stackoverflow.com/questions/5758719/preloading-html5-audio-in-mobile-safari